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Moon and Venus

April 24, 2012

One of the biggest scientific debates of last year was about the leap second -- an extra second that’s sometimes added to the world’s atomic clocks to keep them aligned with Earth’s “wobbly” rotation. The result of a big meeting on the topic was to keep studying it.

We may also need to adjust our clocks for Venus. A spacecraft in orbit around the planet found that a Venusian day appears to be several minutes longer than it was a couple of decades ago.

It’s tough to measure Venus’s day because the planet is veiled by clouds, so it’s impossible to see features on its surface. But in the 1990s, a spacecraft used radar to peer through the clouds. It measured the length of Venus’s day at a bit longer than 243 Earth days.

But Venus Express, a craft that’s orbiting Venus now, found that the day is about six-and-a-half minutes longer than the earlier measurements. Observations by radio telescopes here on Earth also hint at the longer day.

It’s possible that the difference is simply a mistake. But it’s also possible that Venus’s rotation has slowed down. The planet’s atmosphere is much thicker than Earth’s, and as it moves, it creates friction with the surface. Long-term motions of the dense atmosphere could act as a brake, slowing Venus’s rotation and making its day a little longer -- requiring a big adjustment to Venusian clocks.

Look for Venus in the west this evening, to the upper right of the Moon. Venus is the brilliant “evening star,” so you can’t miss it.


Script by Damond Benningfield, Copyright 2012


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